2001 426 Jetting

I absolutely love my 426, but yesterday I took it on a trail ride and it really wasn't running up to par. If I was on the gas hard all was fine, but the low end wasn't as responsive, and it hiccupped and even popped quite a bit between off-on throttle transitions. I was between 1,000 and 3,000 foot elevation. Does anyone have any advice here? The Jetting is stock as is the rest of the bike, but I never noticed this at all at the track, or on an open desert ride.




01 YZ426

After spending the last couple of months or so trying various jet settings, it seems to me that the fuel screw (which works in the opposite manner of the air screw on a 2-stroke) is very outside temperature sensitive. Anything like a 10 degree outside temp change prompts me to adjust the fuel screw slightly to keep the "Bog" blues away. Off the floor, my bike was lean on top and bottom and rich in the middle! My current settings are (3000' ft ele, temp in the 80's) a 165 main, the next leaner needle with the clip in the 4th position from the top and a 45 pilto jet with the screw around 1.5 turns out.

I had similar problems with my 01' 426 last week (at sea level). My problem was that the muffler was empty. After I refilled my muffler with the original muffler stuff (???? sorry I don't know the word) my bike ran fine again. it's probably not the problem you'r having but it may be worth checking.

First the stuff is called packing material. As far a the poping sound when off the throttle, that is normal and has not been a problem with me. The only jetting changes I have made after the new carb from yamaha is to go up one on the needle. It start first kick every time and runs great without fouling a plug. Good luck. I am located in Oregon at 1000' to 2500'.

FYI: I have a 99YZ400F that I ride at 1,000ft and 6,500ft with stock jetting and only notice a very slight loss in output, nor does it load up. My opinion is that the bike was designed to be on it all the time and it might tend to load up a little when trail or tight, slow riding is done, especially at higher altitudes.

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